Piezoelectric crystal oven



May 22, 1956 A. E. MILLER PIEZOELECTRIC CRYSTAL OVEN Filed Oct. 9, 1953 F3. :pl.

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INVENTOR. Huausr E, MILLER H T TORNEYS United States Patent 9 PIEZOELECTRIC CRYSTAL UVEN August E. Miller, Clilfside Park, N. Application October 9, 1953, Serial No. 385,670

12 Claims. (Cl. 219- 19) The invention relates to a piezoelectric crystal oven by means of which the crystal is brought to a desired operating temperature and maintained at that temperature irrespective of the wide variations of outside temperatures, such as -]-90 to 55 C., to which the crystal would otherwise be subjected. It is important that the crystal to be used in an electrical circuit be maintained at a constant temperature in order that the crystal will oscillate at the desired frequency without variation. The range in temperature of operation of a thermostat which controls oven temperature should not be over about two degrees, say within one degree above and below the desired operating temperature. Crystal ovens are provided with a fast heater winding to rapidly bring the oven to approximately its operating temperature and a control winding for maintaining the oven at operating temperature.

It is an object of the invention to construct a piezoelectric crystal oven which maintains the temperature of the crystal at the desired operating temperature within narrow limits and over a very wide variation in the temperature of the external surroundings or ambient.

It is another object of the invention to construct a piezoelectric crystal oven so that the windings of the heater must be properly spaced to give accurate temperature control.

Another object is to construct a crystal oven having a relatively substantial mass of metal spaced from the thermostats which mass forms a heat reservoir to assist in maintaining the crystal at its operating temperature.

A still further object is to construct a crystal oven with posts which serve to locate the heater windings and which also serve as terminal locations.

Another object is to construct a crystal oven with a half turn of the control heater winding adjacent to its thermostat.

Other objects of the invention will be more apparent from the following description when taken in connection with the accompanying drawings illustrating a preferred embodiment thereof in which:

Figure 1 is a side view of a part of a piezoelectric crystal oven showing an internal housing partially in section to show a crystal assembly therein;

Figure 2 is a side view of one side of the oven with the outer housing in section showing the metallic housing upon which the heater windings are wound;

Figure 3 is a side view of the crystal oven similar to Figure 2 and the heater windings taken on the other side from Figure 2;

Figure 4 is an end view of the oven showing the heater windings; and

Figure 5 is a top view of Figure l with a cover removed showing the thermostats for controlling the heater windings.

The crystal oven includes a base 16 having a sufiicient number of contact pins 11 projecting therefrom. It also has a central mounting pin 12 which also carries an electrical contact 13. The base carries a metallic element 14 of as great a mass as space limitations allow which forms a heat reservoir. The metallic element has a hole 15 at each end thereof through which the crystal leads project. An insulating pedestal 16 is secured upon the metallic element which receives an inner insulated housing 17 and retains the housing on the base. The metallic element 14 also serves as a stop for the inner housing 17. The pedestal also carries contacts into which a piezoelectric crystal assembly 18 is plugged. The inner housing sur-. rounds the piezoelectric crystal assembly. The metallic element 14 serves two purposes, namely: to slidably receive a metallic housing 21 upon which heater windings are carried and as a heat reservoir which absorbs heat from the heater windings when they are heating and to give up heat to the surrounding structure when the heaters are not heating as an aid in maintaining the temperature constant. The heat reservoir is at the lower end of the oven and hence spaced from the thermostats to give a proper heat balance to the oven.

The metallic housing 211 surrounds the inner housing and carries heater windings. The housing has an insulator block 22 secured on each side thereof each of which blocks carries a pair of terminals. The terminal 23 is grounded by a wire 27 soldered to the metallic housing. The terminal 26 connects through a wire 28 with one end of a fast heater winding 29 which is wound around the lower end of the housing and terminates at terminal 39. This winding should not extend beyond the upper half thereof and in the construction particularly illustrated, it is in about the lower one-quarter of this housing as measured from the upper end of the insulator blocks. The other end or" the fast winding is connected by a wire 31 to a lead-in 32 which connects with a thermostat to be described hereinafter. The wire 28 is connected with a solder terminal carried on an insulated post 33 which is secured to a side of the metallic housing 21.

One end of a control heating winding 35 is also connected with the terminal 26 by wire 28 and half of its winding parallels the fast heater winding. An insulated post 36 is secured to the metallic housing and at about approximately the mid point of the control winding it turns around the post and the remanider of the winding is Wound in a reverse direction around the metallic housing. The control winding therefore is non-inductive so that it will not aflect the operation of the crystal. The turns of the upper portion of the control winding are widely spaced on the balance of the metallic housing and the end of the winding is connected at the terminal 37 carried on an insulated post 38 secured to the metallic housing. The end of the winding is connected by a wire 39 to a leading connection 4 9 to second thermostat carried at the top of the metallic housing as will be described. it has been found that for accurate control a half to one and a half turns of the control Winding should be positioned adjacent the thermostats and in order to assure this the metallic housing has a pair of projections 41 formed in any suitable way, shown as being struck out from the wall of the housing which locates these turns at the top of the metallic housing and also aids in retaining it against shifting from this position.

The metallic housing is covered with position such as varnish. The heater windings are also suitably insulated. Both heater windings are selected as to wire size and length depending upon the voltage which is to be applied thereto.

A metallic thermostatic housing is fixed to the the metallic housing such as by soldering. To the bottom of the thermostatic housing is soldered a thermostatic frame 44 to which is riveted a pair of thermostats of the bimetallic element type, one being provided for each winding. The thermostat 46 is in circuit with the fast heater winding 29 and thermostat 47 is in circuit with the control an insulating comtop of winding 35. An adjusting screw 48 provides the contact with its respective thermostat bimetallic element and for adjusting the temperature at which the thermostat opens to break the circuit to'its winding. The thermostatic elements are riveted to the thermostatic frame 44 and the frame is soldered to the bottom of housing 45 to assure against distortion and connects both thermostats with the metallic housing and terminal 23. A metallic cover 49 is also soldered over the top of the thermostatic housing.

The lead-in wire from each winding to its respective thermostat is through an insulating nylon bushing secured to the thermostat housing wall.

It is desirable that a light or signal be connected in parallel with each winding to indicate which windings are functioning. This connection for the control winding 35 is a wire 52 which leads to a terminal 2 which is connected with a signal (not shown). The fast heater winding 29 has a wire 53 connected with terminal 30 at the end of the winding which is in turn connected with terminal which terminal is connected with a suitable signal light (not shown).

An outer insulating housing 55 encloses the entire assembly and is secured to the base in any suitable fashion such as by screws 56. There is therefore provided an outer insulating housing within which is a metallic housing carrying the heater windings and thermostats within which is a second insulating housing. The crystal assembly is mounted within the inner housing.

In operation, if the temperature within the oven or thermostats is below operating temperature, both thermostats are closed and both heaters are in operation to raise the temperature of the crystal and crystal oven. When the temperature approaches the desired operating temperature of the oven, the thermostat for the fast heater winding opens to disconnect the same. The control winding continues in operation until the upper limit of operating temperature is reached whereupon its thermostat opens to break the circuit and the control winding is disconnected from the electrical source.

Should the temperature at the thermostats drop to the operating or closing temperature of the thermostat for the control winding, it again closes the circuit and supplies heat to raise the temperature to the temperature at which it again opens to disconnect the control winding.

Successful and accurate control of the temperature of a crystal oven depends upon a proper heat balance within the oven. It has been found that in order to improve the sensitivity and secure close or accurate control of the temperature, that approximately a half turn up to a turn and a half of the control winding should be adjacent the top of the metallic housing and hence adjacent to the thermostat housing 45. The amount of turns is dependent upon the winding used and current therethrough. There cannot be much more or less that the specified turns adjacent the thermostat housing otherwise it will aiifect the sensitivity and accurate control of the thermostat and hence the temperature of the crystal. it is also necessary for accurate control that the upper half of the control winding be spread widely over the upper portion of the metallic housing. The upper portion or half of the control winding 35 is spread over three-quarters of the one inch of the length of the metallic housing as measured from the end of the insulating blocks to the end of the metallic housing which is the bottom of the thermostatic housing. The fast heater winding is wound around the lower onequarter inch of the housing. The location of the heat reservoir also affects accurate heat balance between the elements whereby accurate temperature control is secured. The location of the insulated post 35 therefore provides a boundary post below which the fast heater winding is to be located and above which the upper half of the control winding is to be spread for accurate control of the temperature of the crystal.

The invention is presented to fill a need for improvements in a Piezoelectric Crystal Oven. It is understood that various modifications in structure, as well as changes in mode of operation, assembly, and manner of use, may and often do occur to those skilled in the art, especially after benefiting from the teachings of the invention. Fence it will be understood that this disclosure is illustrative of preferred means of embodying the invention in useful form by explaining the construction, operation and advantages thereof.

What is claimed is:

l. A piezoelectric crystal oven comprising a base, an inner insulating housing carried on the base within which a crystal assembly is received, a metallic housing mounted on the base and surrounding the inner housing, a pair of thermostats carried upon the upper end of the metallic housing, a fast heater winding around the lower end of the metallic housing solely and connected with one thermostat, the fast heater winding being substantially spaced from the thermostats, a control winding around the metallic housing and extending the length thereof and connected with the other thermostat, and an outer insulating housing mounted on the base.

2. A piezoelectric crystal oven as in claim 1 including a metallic element of substantial mass carried by the base and conforming in shape with the lower end of the metallic housing to receive the same.

3. A piezoelectric crystal oven comprising a base, an inner insulating housing carried on the base within which a crystal assembly is received, a metallic housing mounted on the base and surrounding the inner housing, a pair of thermostats carried upon the upper end of the metallic housing, a fast heater winding around the lower end of the metallic housing and connected with one thermostat, a control winding around the metallic housing and extending the length thereof and connected with the other thermostat, including a half turn of the control winding being adjacent to thermostats, and an outer insulated housing mounted on the base.

4. A piezoelectric crystal oven as in claim 3 including a pair of spaced projections on one side of the metallic housing adjacent to the upper end thereof to locate and retain the half turn of the control winding in position.

5. A piezoelectric crystal oven comprising a base, an inner insulating housing carried on the base within which a crystal assembly is received, a metallic housing mounted on the base and surrounding the inner housing, a pair of thermostats carried upon the upper end of the metallic housing, a fast heater winding around the lower end of the metallic housing and connected with one thermostat, a control winding around the metallic housing and extending the length thereof and connected with the other thermostat, and an outer insulating housing mounted on the base, including a post carried by the outer side wall of the metallic housing between the ends and on the lower half thereof, and the control winding approximately at its center passing around the post to reverse the direction of the winding and locate half of the winding on the upper portion of the metallic housing.

6. A piezoelectric crystal oven as in claim 5 including a terminal on the post for the end of the fast heating winding, and a connection between the terminal and its thermostat.

7. A piezoelectric crystal oven as in claim 5 including an insulated post at the upper end of the metallic housing providing a terminal for the control winding.

8. A piezoelectric crystal oven as in claim 5 including the last half turn of the control winding being located at the top of the metallic housing adjacent to the thermostats.

9. A piezoelectric crystal oven as in claim 8 including a metallic element of substantial mass carried by the base and to receive the metallic housing.

10. A piezoelectric crystal oven as in claim 9 including an insulated post carried by the outer lower end of the metallic housing and forming a terminal for both windings.

11. A piezoelectric crystal oven as in claim 10 including an insulated post carried by the outer upper end of the metallic housing and forming a terminal for the control winding.

12. A piezoelectric crystal oven as in claim 3 including a metallic element of substantial mass carried by the base and conforming in shape with the lower end of the metallic housing to receive the same.

References Cited in the file of this patent UNITED STATES PATENTS 

